Starch makes up approximately 70% of the dry weight of cereal grains and is composed of two forms of glucose polymers, straight chained amylose with α-1,4 linkages and branched amylopectin with α-1,4 linkages and α-1,6 branch points. In bread wheat, amylose accounts for approximately 25% of the starch with amylopectin the other 75% (reviewed in Tetlow 2006). The synthesis of starch granules is an intricate process that involves several enzymes which associate in complexes (Tetlow et al. 2008; Tetlow et al. 2004b). In bread wheat, the “waxy” proteins (granule bound starch synthase I) encoded by the genes Wx-A1a, Wx-B1a, and Wx-D1a are solely responsible for amylose synthesis after the production of ADP-glucose by ADP-glucose pyrophosphorylase (AGPase) (Denyer et al. 1995; Miura et al. 1994; Yamamori et al. 1994). In contrast, amylopectin synthesis involves a host of enzymes such as AGPase, starch synthases (SS) I, II, III, IV, starch branching enzymes (SBE) I and II, and starch de-branching enzymes (Tetlow et al. 2004a).
The majority of durum wheat is used for pasta and pasta products, but there is interest in investigating durum wheat for noodle production. There are several reasons for interest in durum noodle production. First, it would provide an additional market for durum wheat grain. Durum wheat is lower than bread wheat in polyphenol oxidase, an enzyme causing noodles to turn gray or brown with time. Finally, the high level of carotenoids present in durum wheat could produce enhanced yellow color for alkaline noodles. The proportion of amylose to amylopectin is an important factor in determining end product properties in durum wheat. Much attention has been devoted to determining the impacts of reduced amylose on Asian noodle quality in bread wheat. Information is lacking on the impacts of small increases in amylose on end product quality in durum wheat. Therefore, there is a great need in compositions and methods of modifying amylose in durum wheat. The present invention provides compositions and methods for producing improved durum wheat plants through conventional plant breeding and/or molecular methodologies.